If the AC power source is connectedto the resistor, then the current and voltage in the circuit at any point in the time diagram will be proportional to each other. This means that the current and voltage curves will reach a "peak" value at the same time. At the same time we say that the current and voltage are in phase.
Let us now consider how the capacitor behaves in the AC circuit.
If an AC voltage source is connectedcapacitor, the maximum value of the voltage on it will be proportional to the maximum value of the current flowing in the circuit. However, the wave peak of the voltage sinusoid will not attack at the same time as the maximum current.
In this example, the instantaneous current reachesits maximum value for a quarter of the period (90 el.grad.) earlier than it will make the voltage. In this case, they say that "the current is ahead of the voltage by 90 °."
Unlike the situation in the DC circuit,The value of V / I is not constant here. Nevertheless, the ratio V max / I max is a very useful value and in electrical engineering is called the capacitive resistance (Xc) of the component. Since this value still reflects the ratio of voltage to current, i.e. in the physical sense is resistance, its unit of measurement is Om. The value Xc of the capacitor depends on its capacitance (C) and the frequency of the alternating current (f).
Since the capacitor in the alternating current circuitthe root-mean-square value of the voltage is applied, in this circuit the same alternating current flows, which is limited by the capacitor. This limitation is due to the reactance of the capacitor.
Therefore, the current in the circuit, which does not contain any other components other than the capacitor, is determined by an alternative version of Ohm's Law
ANDRMS = YRMS / XFROM
Where URMS - rms voltage value. Note that Xfrom replaces the value of R in the version of Ohm's law for direct current.
Now we see that the capacitor in the circuitAC behaves quite differently than a constant resistor, and the situation here, accordingly, is more complicated. In order to better understand the processes occurring in such a chain, it is useful to introduce such a concept as a vector.
The main idea of a vector is the idea that,that the complex value of the time-varying signal can be represented as the product of a complex number (which does not depend on time) and some complex signal that is a function of time.
For example, we can represent the function A cos (2πνt + θ) simply as a complex constant A ∙ ejΘ .
Since the vectors are represented by a magnitude (or modulus) and angle, they are represented graphically by an arrow (or vector) rotating in the XY plane.
Taking into account that the voltage on the capacitor"Lags" in relation to the current, representing their vectors are located in the complex plane as shown in the figure above. In this figure, the current and voltage vectors rotate in a direction opposite to the clockwise direction.
In our example, the current on the capacitor is due toits periodic recharge. Since the capacitor in the AC circuit has the ability to periodically accumulate and discharge an electric charge, there is a constant exchange of energy between it and the power source, which in electrical engineering is called reactive.
